1. Field of the Invention
The present invention relates to a wheel support bearing assembly for use in an automotive vehicle and, more particularly, to the wheel support bearing assembly including an electric generator that serves as a means for detecting the number of revolution for an anti-skid braking mechanism.
2. Description of the Prior Art
An anti-skid brake device (ABS), also referred to as an anti-lock brake device, is known as used for detecting the incipiency of a tire lock occurring on a low frictional road surface or at the time of a panic stricken braking so that braking can be relieved to secure a tire grip to thereby stabilize the steerability. A sensor for detecting the number of revolutions of a wheel for detecting the incipiency of the tire being locked is provided in a wheel support bearing assembly. This sensor generally includes a pulsar ring provided at an end portion or the like of a raceway in a bearing outside, and a sensor portion provided in face-to-face relation with the pulsar ring.
Also, as a wheel support bearing assembly having the sensor built therein, such a bearing assembly as shown in FIG. 35 has hitherto been suggested in, for example, the Japanese Laid-open Utility Model Publication No. 1-156464. This known wheel support bearing assembly includes, as shown in FIG. 35, a sensor portion 57 incorporated in a bearing outer race 51 which serves as a stationary member. This known bearing assembly also includes an outer race 51 for securement to a vehicle body structure, an inner race 52 mounted on a shaft portion of a hub wheel 54, a plurality of rolling elements 53 interposed between the inner race 51 and the outer race 52, and a sealing member 60. The rotation sensor 55 is of a structure wherein the sensor portion 57 is inserted into a hole 58 defined in the outer race 51 so as to confront and align with the pulsar ring 56 that is rigidly mounted on an outer peripheral surface of the inner race 52. The use of the sensor built in the bearing assembly is effective to reduce the size of the wheel support bearing assembly as compared with the arrangement in which the pulsar ring and the sensor portion are disposed at the end of the bearing outside.
In the prior art wheel support bearing assembly having built therein the sensor for detecting the number of revolutions of the wheel, a wired interfacing system is generally employed in which detection signals generated by the sensor and supply of an electric power to the sensor are interfaced with the vehicle body structure by means of a wiring. This is not an exception to the known wheel support bearing assembly shown in FIG. 35, in which signal interfacing and supply of the electric power are carried out by means of an electric cable 59. As such, the known wheel support bearing assembly makes use of the electric cable for drawing a sensor output, and this electric cable is exposed to the outside of the vehicle body structure at a location between the wheel support bearing assembly and the vehicle body structure. Because of this, the electric cable is susceptible to breakage by the effect of stones hitting and/or frozen snow within a tire housing. Also, in the case of a steering wheel, not only is it necessary for the electric cable to be twisted beforehand, but often times a relatively large number of processing steps is required. The electric cable referred to above also requires a sheathing thereof and, therefore, reduction in weight of an automotive vehicle tends to be hampered and, in view of the large number of steps of fixing the electric cable, a high cost tends to be incurred.
Also, although the known wheel support bearing assembly of the type in which the sensor is built therein as shown in FIG. 35 can be assembled relatively compact, servicing of the rotation sensor 55 requires dismantling of the outer and inner races 51 and 52 of the wheel support bearing assembly, resulting in a problem that the servicing cannot be performed efficiently. For this reason, once the rotation sensor 55 fails to operate, the wheel support bearing assembly as a whole would be required to replace with a new one. In addition, although the known wheel support bearing assembly shown in FIG. 35 is of the type wherein the rotation sensor is built therein, since the sensor portion 57 is partly exposed outside the bearing assembly, no sufficient reduction in size thereof is still achieved. Yet, the known wheel support bearing assembly shown in FIG. 35 has a problem in that sealing of the hole 58 defined in the outer race 51 for receiving the sensor portion 57 is difficult to achieve, making it difficult to prevent any ingress of foreign matter.
In order to alleviate the foregoing problems, it may be contemplated to use a wireless interfacing system such as disclosed in, for example, the Japanese Patent Application No. 11-339588. According to this application, the rotation sensor used therein is of a type capable of transmitting signal wireless to a receiver. In this wireless interfacing system, the modulation and the directionality of the transmitted waves are carefully selected so that the signal transmitted wireless from the rotation sensor will not be affected adversely by external jamming radio waves.
However, even with the wireless interfacing system, any countermeasures against the external jamming radio waves are insufficient, and so is with illegal high power radio waves that are difficult to suppress. As a result, there is no way of determining whether or not the wireless transmitted signal indicative of the number of revolution of the wheel has been affected by the external jamming radio waves and, hence, there is a high risk that the braking force cannot be properly controlled.